#include <iostream>
#include <vector>
#include <set>
#include <queue>
#include <cstdio>
#define DN 500005
using namespace std;

typedef vector<int>::iterator it;
typedef set<int>::iterator is;

vector<int> gr[DN];
int n,m,d[DN];
long long bc,a,b;
queue<int> c;

void bfs() {
  d[1]=1;
  for(int i=2; i<=n; ++i) d[i]=0;

  for(c.push(1);!c.empty(); c.pop()) {
    int fr=c.front();
    for(it i=gr[fr].begin(); i!=gr[fr].end(); ++i) if(!d[*i]) {
      d[*i]=d[fr]+1;
      c.push(*i);
    }
  }
  if(d[n]!=0) bc=min(bc,(d[n]-1)*a);
}

void tbfs() {
  set<int> na;
  d[1]=1;
  for(int i=2; i<=n; ++i) {
    d[i]=0;
    na.insert(i);
  }
  for(c.push(1);c.size(); c.pop()) {
    int fr=c.front();
    set<int> nb;
    for(it i=gr[fr].begin(); i!=gr[fr].end(); ++i) if(d[*i]==0)
      nb.insert(*i);
    for(is i=na.begin(); i!=na.end();)
      if(d[*i]==0 && nb.find(*i)==nb.end()) {
        d[*i]=d[fr]+1;
        c.push(*i);
        is j=i;
        ++i;
        na.erase(j);
      }else {
        ++i;
      }
  }
  if(d[n]!=0) bc=min(bc,(d[n]-1)*b);
}

int main() {
 // freopen("input.txt","r",stdin);
  while(cin>>n>>m>>a>>b) {
    for(int i=1; i<=n; ++i)gr[i].clear();
    int dir=b;
    for(;m--;) {
      int x,y; cin>>x>>y;
      if((x==1 && y==n) || (x==n && y==1)) dir=a;
      gr[x].push_back(y);
      gr[y].push_back(x);
    }
    bc=dir;
    bfs();
    tbfs();
    cout<<bc<<'\n';
  }
}